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我想寫一個聯繫程序，用戶按下按鈕添加一個聯繫人（第二個活動）。我不斷收到同樣的錯誤：常見的android錯誤，其他答案沒有幫助！ java.lang.NullPointerException：
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
我已經看了很多其他的答案，但我就是無法找到爲什麼我的代碼，特別是不能正常工作。
這是我的主要活動的java：
public class MainActivity extends AppCompatActivity {
private ListView lvContact;
private Button bt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final List<ContactBook> listContactBook = new ArrayList<ContactBook>();
lvContact = (ListView)findViewById(R.id.listcontact);
final ContactBookAdapter adapter = new ContactBookAdapter(this, listContactBook);
lvContact.setAdapter(adapter);
lvContact.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
Intent intent = new Intent(getApplicationContext(), secondActivity.class);
startActivity(intent);
}
});
try {
bt = (Button) findViewById(R.id.add);
bt.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getApplicationContext(), secondActivity.class);
startActivity(intent);
}
});
}
catch(NullPointerException e){
System.out.checkError();
}
這是我的Java爲我的第二個活動
public class secondActivity extends AppCompatActivity {
private ListView lvContact;
private Button bt;
private EditText first;
private EditText mid;
private EditText last;
private EditText phone;
private EditText birth;
private EditText meeting;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
final List<ContactBook> listContactBook = new ArrayList<ContactBook>();
lvContact = (ListView)findViewById(R.id.listcontact);
final ContactBookAdapter adapter = new ContactBookAdapter(this, listContactBook);
lvContact.setAdapter(adapter);
//get data
first = (EditText)findViewById(R.id.firstName);
mid = (EditText) findViewById(R.id.midInitial);
last = (EditText) findViewById(R.id.lName);
phone = (EditText) findViewById(R.id.pNumber);
birth = (EditText) findViewById(R.id.bDay);
meeting = (EditText) findViewById(R.id.fMeeting);
bt = (Button) findViewById(R.id.save);
bt.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String newf, newi, newl, newn, newb, newd;
newf = first.getText().toString();
newi = mid.getText().toString();
newl = last.getText().toString();
newn = phone.getText().toString();
newb = birth.getText().toString();
newd = meeting.getText().toString();
listContactBook.add(new ContactBook(newf, newi, newl, newn, newb, newd));
adapter.notifyDataSetChanged();
}
});
}
我的清單
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".secondActivity"
android:label="@string/title_activity_second"
android:theme="@style/AppTheme.NoActionBar"></activity>
</application>
我知道這是一個非常常見的錯誤我應該能夠找到它，但由於某種原因，我不能，無論我嘗試什麼。
謝謝！
編輯： 這裏是完全錯誤日誌：
I/PhoneWindow: [setNavigationBarColor2] color=0x ff000000
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.bignerdranch.android.contactapp, PID: 16741
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bignerdranch.android.contactapp/com.bignerdranch.android.contactapp.secondActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2378)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2440)
at android.app.ActivityThread.access$800(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1348)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5422)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:914)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:707)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.bignerdranch.android.contactapp.secondActivity.onCreate(secondActivity.java:37)
at android.app.Activity.performCreate(Activity.java:6057)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2331)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2440)
at android.app.ActivityThread.access$800(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1348)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5422)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:914)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:707)
可能重複[什麼是NullPointerException，以及如何解決它？]（http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-doi-i-fix -it） –
顯示完整的錯誤日誌。 – TruongHieu
用完整的錯誤日誌編輯的問題！ –